1. Field of the Invention
The present invention generally relates to a developing apparatus for in use an electrophotographic copying apparatus, a printer or the like.
2. Description of the Prior Art
Many of the patents issued in various countries disclose a developing apparatus having a regulation member, which is pressed slidingly against a developing roller for the supply of the toner towards the developing process directory or indirectly. The regulation member is operable to form an electrically charged toner layer on the peripheral surface of a developing roller.
For example, Japanese Patent Application SHO 62-17774, published Jan. 26, 1987, discloses a regulation blade having a generally orthogonally bent end. An outer surface of the bent corner is pressed slidingly against a developing roller. However, because this blade is brought into a line contact with the developing roller, a nip (contact) width between the bent corner of the regulation blade and the developing roller is so small as to result in insufficient electric charging of toner. Furthermore, it is impossible to form a uniform thin layer of toner stably in service over a long time because of the influence which would be brought about by the adhesion of toner to the regulating portion of the blade.
Furthermore, U.S. Pat. No. 4,566,402 discloses the use of two regulation blades of different constructions. One blade is constructed by two pieces of elastic plates bonded at one end with each other. The other blade is constructed by a single elastic plate which is bent at center portion thereof. Both blades are slidingly pressed against the developing roller at their end portion apart from the bonded or bent portion respectively. However, each of these blades can not contact uniformly the developing roller over the entire length of the roller over because the respective blade is flexible and deformable. Therefore this hampers the uniform formation of toner layer and hence results in a varying density of copied image.